What inspires the willingness of humans to make their greatest exertions, to fight unto death with and for genetic strangers, a propensity to which no creature but humans seems subject? What determines the “fighting spirit” that enables one group of combatants to defeat another, all other things being equal? These are basic questions about human nature and warfare that an article by Whitehouse et al. endeavors to address (1). However, that article’s arguments also bear directly on some of the world’s current and most pressing crises. Thus, in recent remarks, President Obama (2) endorsed the judgment of his US National Intelligence Director: “We underestimated the Viet Cong… we underestimated ISIL [the Islamic State] and overestimated the fighting capability of the Iraqi army…. It boils down to predicting the will to fight, which is an imponderable” (3). However, if Whitehouse et al.’s (1) measures and findings are reliable and right, predicting who is willing to fight and who isn’t could be ponderable indeed.

Among American military psychologists (4), historians, and sociologists, conventional wisdom on why soldiers fight is because of leadership and, more important, group loyalty resembling love of family but perhaps even stronger (5). As William Manchester put it in his memoirs of US Marine Corps service in World War II: “Those men on the line were my family, my home. They were closer to me than… friends had ever been or would ever be. They never let me down, and I couldn’t do it to them” (6). Now, using the theory of identity fusion and its associated methods, Whitehouse et al. (1) provide a convincing empirical demonstration of this sentiment as essential to the fighting spirit of combatants who keep risking their lives for their company of imaginary kin, their “band of brothers.”

Until now, fusion theory and methods had only been tested in classroom, laboratory, and online studies: revealing how personal and group identities collapse into a unique identity to generate a collective sense of invincibility and special destiny, especially when the collective is conceived as a small tight-knit group of fictive kin (7). In-depth case and field studies of terrorist groups, of how they developed and how their attacks germinated, also indicate that militants kill and die “for each other… their imagined family of genetic strangers—their brotherhood” (8). However, by applying fusion theory to a field study of revolutionary combatants in Lybia, Whitehouse et al. (1) show in replicable ways that “family-like” social bonds, which indissociably wed personal identity to group identity, may well enable combatants to fight on, even in the face of death and defeat.

Those who study “fighting spirit” in the military tend to chalk up “the semi-mystical bond of comradeship” to rational self-interest (9), and to dismiss any idea of sacrifice for a cause as a critical factor in war. In Vietnam, for example, American soldiers told interviewers that the cause of democracy was “crap” and “a joke.” However, they described the selfless bravery of the Viet Cong and North Vietnamese “because they believed in something” and “knew what they were fighting for” (10). Perhaps, then, some do fight and die for a cause, as well as comrades, and that is why they win wars.

Although the evidence in Whitehouse et al. (1) suggests that identity fusion with a close family-like group is strongly associated with willingness to fight and die, fighters also claim they do so for a greater cause. As Darwin surmised in The Descent of Man (11), it is not merely commitment to a tribe of imagined kin but also to its “morality” that instills “the spirit of patriotism, fidelity, obedience, courage, and sympathy” with which winning groups are better endowed in history’s spiraling competition for survival and dominance. Studies across cultures suggest that the strongest forms of primary group identity are bounded by sacred values (12), often in the form of religious beliefs or transcendental ideologies (13), which leads some groups to prevail because of nonrational commitment from at least some of its members to actions that drive success independent—or all out of proportion—from expected rational outcomes (14). For such “devoted actors,” rightness of in-group cause often leads to intractable conflicts with out-groups that become immune to the give-and-take common to “business-like” negotiations (15).

Thus, our interviews with United States officials familiar with Abu Bakr al-Baghdadi (now self-proclaimed “Caliph” of the Islamic State) and his close circle, including General Douglas Stone, who commanded Camp Bucca where they were held, suggests absolutely committed “purists,” completely devoted to their idea of Sharia and the Caliphate, and willing to do anything for it, to use violence to instill blood lust among their followers and terror among enemies, who were no match for them. Unconditional commitment to comrades, in conjunction with their sacred cause, may be what allows low-power groups to endure and often prevail against materially stronger foes: since World War II, revolutionary and insurgent groups (e.g., the Islamic State) have beaten armies with up to an order-of-magnitude more firepower and manpower because of devotion to comrade and cause rather than typical reward structures, like pay and promotion (e.g., Iraq’s army) (16).

One drawback in the article by Whitehouse et al. (1) is lack of a comparison group: practically everyone is fused and involved in the fighting, a situation similar to that of the Kurds on the front lines around Mosul in Iraq where our research team is currently working. This aspect precludes strong conclusions about the path and process from fusion to willingness to fight. Studying susceptible populations before engagement with active violence and battle can help fill this gap. Consider the following:

Upwards of 2,000 Moroccans have joined jihadi groups in Syria, primarily the Islamic State, and our field discussions with Moroccan officials indicate that scores of volunteers are now leaving monthly from some Moroccan towns. Systematic analysis of dialogues in social media among hundreds of foreign fighters over the last 3 y indicates a marked shift in motivations over the last year from saving coreligionists in Syria to establishing Sharia and securing the Caliphate, regardless of the wishes of local populations (17). Moroccan volunteers conform to the pattern.

As previously with al-Qaeda volunteers from the diaspora (18), about three of every four foreign fighters in Syria volunteer in clusters of friends (19), some attuned to the cause through social media and arriving in groups, and some being drawn to the cause by friends already in place or who have returned to their point of origin. In surveys of two Moroccan communities associated with militant jihad (20), and where we had done intensive anthropological fieldwork, we used the same fusion measure as Whitehouse et al. (1) and a sacred value measure adapted from a previous publication in PNAS (14). We found that that fusion with family-like groups may drive costly sacrifices expressed, for example, in willingness to use violenceThe evidence in Whitehouse et al. suggests that identity fusion with a close family-like group is strongly associated with willingness to fight and die.and to die. However, such willingness appears likely to increase significantly for those who also hold a sacred value (Fig. 1).

Two factors, identity fusion and sacred values, interact to determine who is likely to become a devoted actor based on expressions of willingness to make costly sacrifices, including fighting and dying. In this graph summarizing results from a Moroccan community surveyed with links to militant Jihad (20), only those subjects who were fused with a family-like group and considered Sharia a sacred value were more willing than not to make costly sacrifices, being above the midpoint of a 7-point response scale, from strongly unwilling to strongly willing. (Error bars show 95% confidence levels.)

These findings support Whitehouse et al.’s (1) core argument that fusion plays an important role in galvanizing willingness for extremely costly actions by “devoted actors” characteristic of revolutionary and insurgent groups; however, the findings also suggest that devoted actor groups rally around sacred values—as when law or land become holy or hallowed—to induce high levels of sacrifice. To explain their result that fighters “express stronger fusion with battalions than nonfighters,” Whitehouse et al. speculate that “fusion with the battalion may have caused people to volunteer” (1). Our surveys, combining Whitehouse et al.’s measure of identity fusion with a measure of sacred value, provide a different process to explain their results: a cluster of friends or fellow travelers may come to hold sacred values, perhaps initially influenced by one or a few of them, and then fuse into an​ imagined family-like group defined and driven by these values. Furthermore, when sacred values are at the core of motivations to make extreme sacrifices, it becomes clear how people can sustain commitment and continue to fight. This result is so even when most of the group they were fused with has perished, as Darwin intimated in his discussion of heroism and martyrdom under low initial probability of victory or even group survival (11).

Acknowledgments

We thank ARTIS Research and the US Department of Defense MINERVA Initiative for support.

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